ESR1 and breast cancer: The internal cohort comprised 306 patients with breast cancer with the following characteristics: the majority (204/306, 66.7%) were aged 40-60 years, 94.8% (290/306) had invasive ductal carcinoma, and receptor status analysis revealed 59.5% (182/306) estrogen receptor (ER)+, 58.5% (179/306) progesterone receptor (PR)–, and 30.7% (94/306) human epidermal growth factor receptor 2 (HER2)+ cases.